Aug.11 (GMM) Less than two weeks after shocking the F1 world with his comeback plan, Michael Schumacher shocked the sport's inhabitants again on Tuesday by calling it off.

The 40-year-old German crashed a German Superbike during testing in February, but until now the details of his injury were not known.

"It was the most serious accident in Michael's motor sport career," his manager Willi Weber told the German news agency DPA on Tuesday.

Schumacher revealed on his website that the crash had caused fractures in the area of his head and neck.

But the sceptics also had a voice on Tuesday, one writing in Britain's Guardian newspaper that "only Michael Schumacher knows if the biggest hurt during a comeback would have been to his neck or his pride".

Schumacher's younger brother Ralf hit back in the pages of Bild newspaper: "Fractures in the vertebrate are not something to be dismissed lightly."

The seven time world champion's decision also moved the conversation on to the next replacement for injured Felipe Massa: 38-year-old Italian Luca Badoer, who has been Ferrari's test driver for more than a decade.

Carlos Gracia, president of the Spanish motor racing federation, slammed the Maranello team's decision to overlook its other tester, Spaniard Marc Gene.

"It's an absurdity by the management of Ferrari," he said in the sports newspaper Marca. "Gene is better prepared and has just won the 24 hours of Le Mans."